During treatment with continuous positive airway pressure (CPAP), optimal re-expansion of lung units with minimal work of breathing is best accomplished when the airway pressure (Paw) is kept constant at the desired CPAP level throughout the entire breathing cycle. To achieve this, a new device was constructed in which CPAP was generated by a jet of fresh gas close to the nasal airway. The performance of the new device was investigated experimentally using a lung model which simulated the breathing pattern of a newborn. Paw, flow, and external work of breathing were measured at three CPAP levels, with and without controlled airway leakage. The new device was compared with a traditional continuous-flow CPAP system with standard nasal prongs. Despite a virtually constant pressure within the traditional system, Paw variations and external workload were considerably less with the new device, which was also less sensitive to airway leakage.